"Using" a magic item means... using it

The "Using a Magic Item" section of the rules explains what "using a magic item" entails:

A magic item’s description explains how the item works. Handling a magic item is enough to give a character a sense that something is extraordinary about the item. The identify spell is the fastest way to reveal an item’s properties. Alternatively, a character can focus on one magic item during a short rest, while being in physical contact with the item. At the end of the rest, the character learns the item’s properties, as well as how to use them. Potions are an exception; a little taste is enough to tell the taster what the potion does.

The paragraph begins with "magic items", not qualified by "some magic items". From this we can deduce that all magic items are "used" in order to use them. Since potions are given as an example, we clearly know potions are "used". How about attuned items? The section on attunement goes on to say:

Some magic items require a creature to form a bond with them before their magical properties can be used.

So attuned items are used too.

5e actually did away with the old keyword "use", and seemingly replaced it with "activate":

Activating some magic items requires a user to do something special, such as holding the item and uttering a command word. The description of each item category or individual item details how an item is activated. Certain items use the following rules for their activation.

Use Magic Device is plain English

Players aren't meant to read into it, or port terms from older editions. "Use" just means "use"; it's plain English.

If an item says it requires attunement by a Elf, then "Elf" is a race requirement to use the item. A human Thief rogue could ignore this requirement in order to use it.

Beware using new rules to retcon old rules

The rogue's rules were written 5 years before the artificer released. There is no reason to think that the artificer was written to affect the Thief rogue in any way.

When considering how rules work, I find it best to examine the rule and all rules that govern it. If that is somehow unsatisfactory, then compare other wordings from the same and previous source books.

I think your interpretation is correct, so no, it doesn't ignore attunement requirements

The artificer's Magic Item Savant feature says, in part:

You ignore all class, race, spell, and level requirements on attuning to or using magic items.

The Thief rogue's Use Magic Device feature says:

You ignore all class, race, and level requirements on the use of magic items.

Given that they are worded so similarly, with the key difference being "attuning to or using" vs. "using", I would interpret that to mean that the Artificer can ignore class, race, spell, and level requirements for both attuning and using magic items, while the Thief rogue can ignore class, race, and level requirements for the use only.

From a lore perspective, this makes sense, as the Artificer is focused on magic gizmos and items, while the Thief rogue has worked out how to use magic items through handling so many. One is a class that has a focus on magical items, and for the other it is incidental.

If it weren't for the artificer specifying attunement, I would have probably interpreted Use Magic Device as allowing attunement, but given that Magic Item Savant specifies attunement, it is more clear that the Thief cannot use this feature to ignore attunement requirements.