One of the benefits of being an expert in a particular field, is that you can take small parcels of evidence and formulate an accurate picture of a situation much faster than a layman with no prior experience in that field. I don't know the anthropologist in question, but I am sure she used a series of supporting evidence that was obvious to her trained eye as well as the teeth condition.

Ask any doctor or midwife who can look at an ultrasound image and tell you the sex of the baby while you are still staring at a smudgy grey moving image. Ask any accident investigator who can estimate the speed and trajectory of the vehicles while you are still looking for the skid marks.

I personally have spent over 25 years interacting on public message boards, and I am a domain expert enough that I can pick an armchair expert who has lots of perceived theoretical knowledge, but little or no real world knowledge, but still feels the need to espouse their opinion in order to get their dopamine hit of the day - all just from a quick glance at their post.

I agree it sounds like bullshit.

However, I have listened to a talk by a lady (she consults on murdered cadavers) who can tell which season a body died in by analyzing the teeth! Apparently there is a lot there.

That I can believe, assuming a detailed analysis in a lab. But snap judging from a distance? Cavities are more common in modern populations than before, but hardly omnipresent. I do find it an amusing thought that apparently my skeleton would be assigned a more distant past simply because I am filling free. :D

It might be not that hard for someone who's literal job is examining skeletal remains.

The more likely sign is not fillings, but acid damage, which softens teeth and cause biting and grinding to wear down the surface of the teeth. You can have no fillings and still have very noticeable acid-related damage.