[ablanco]

It would be nice to understand how you came to the conclusion that this was a Facebook bot.

[napolux]

Ip addresses.

for example https://www.ultratools.com/tools/ipv6InfoResult?ipAddress=2a...

[akerro]

You can check list of IP addresses?

[huac]

the OP did not (explicitly) check, but you can check if the IP falls into a range allocated to Facebook e.g. https://ipinfo.io/AS32934

[napolux]

Of course I've checked. Here is a recent example. https://news.ycombinator.com/item?id=23491455