at what point does lunch become a regular meeting? Or is the whole
lunch meeting just considered lunch? If we didn't have to record our
time at work and time on breaks this wouldn't really be an issue but
since we do I am unsure.
Every company has different policies regarding what must be recorded and in which categories time is recorded.
If neither you nor your colleague know how to categorize this time, ask someone who does - that might be your manager, or someone else responsible for timekeeping.
Some companies use this time to charge external clients for projects and have contractual rules surrounding time recording. Some use this time to input into payroll. Some companies do both.
In my most recent shop, it seldom mattered how your time was recorded, as long as it added up to 40 hours per week. In other shops where I worked, time recorded against specific projects was very precious and they worried about every 30 minutes. In most shops where I worked, lunch time would never be recorded, even if you talked about work or actually performed work.
Don't overthink things. I'm not saying any of this makes sense, or that any of this will amount to a sensible ledger of time spent. Just that every company defines their rules differently, and you will have to ask until you have learned them.
Every timekeeping system has ambiguities (what if you think about work while you are eating alone? What if you spend only 10 minutes talking about work and the rest eating? What if you talk about projects that don't have accounting codes assigned yet?). You just need to learn how your management wants you to handle these situations. I don't see a lot of commonality across companies.