I have been to sing-alongs where a man, the leader, chooses to start in a low pitch (low for me as a tenor).
I can't sing that low. Why would a man choose a very low key for a sing-along? I mean, when you sing solo it is another thing, but it is as if they sing low so that other people cannot sing.
Too low is everything under Bb2. They sing A2 or Ab2.
Reasons for starting too low:
Vocal range is somewhat dependent on language and culture. Check out where this popular Finnish melody starts: https://virsikirja.fi/virsi-971-maan-korvessa-kulkevi-lapsosen-tie/
It would be an enlightenment to pose the question to the guy concerned. But more than likely, he just pitches at what he thinks is o.k., not having absolute pitch, and not being aware that what he's doing may not be the best.
We had a director of music in the county I taught in, and he would always sing falsetto when leading choirs, in the strange belief that because the pre-pubescent children's voices had not broken, they wouldn't be able to sing in another octave. Personally, I've never found that to be a problem - people naturally sing in whatever octave they find comfortable, even jumping the octave when a note is uncomfortably high or low, due to a small range, usually. Frequently, if I felt that the key didn't suit the singers, I'd change it, so everyone was happy.
I remember being at a school during singing practice, (not as the music teacher), and the music teacher was teaching a song that had quite a high range. He asked what should they do to reach the high notes, and suggested shoulders back, etc. I very nearly interrupted to suggest 'drop the key', but didn't...
People's voices are all different. I've noticed that on average men tend to prefer higher keys than women but there is a great deal of variation.
My own experience is that trying to sing lower than my 'good' range (i.e. below A in the bottom space of the bass clef) just results in poor tone and volume, but never any discomfort, whereas the same is most certainly not true if I try to force myself to sing above middle C.
On that basis, I'd say your friend is probably doing the right thing by erring on the low side. No pitch will suit everyone, but at the very least you don't want to cause anyone to strain their voice by asking them to sing too high.
