Bring sth forward

Until this discovery, the lynx – a large spotted cat with tasselled ears – was presumed to have died out in Britain at least 6000 years ago, […] If this is so, it would bring forward the tassel-eared cat’s estimated extinction date by roughly 5,000 years.

The summary of this paragraph is that

The lynx survived in Britain longer than was previously thought.

As clearly shown in Cambridge Dictionary, the meaning of bring sth forward is that to change the date or the time of event so that it happens earlier than planned.
My teacher explained that “bring forward the lynx’s extinction date by 5,000 years” means that it died out just 1,000 years ago instead of 6,000 years. If the year of extinction was presumed to be 4000 BC, then it was proved to be around 1000 AD. It confused me because if so, the extinction of this species happened later than expected but not earlier. I expect it would be 11000 BC, since it happened earlier than estimated by 5,000 years. Therefore, it died earlier than was previously thought.
Maybe there’s something wrong with my calculation but not the language. I just can’t figure it out.