Are you in the US? No one uses whatsapp in the US. This would have been done as an sms groupchat in all likelihood. Everything friends plan is on sms these days. Maybe its my generation, we don’t like signing up for accounts anymore when everyone can trivially text.
Your comment made me breathe a sigh of relief, because my kids are rapidly approaching “I need to communicate with their friends’ parents” age, and I don’t think I have it in me to sign up for WhatsApp. I’m in the US and I’m ok just texting. iOS supports RCS now, it’s good enough.
I actually took the time to sign up for WhatsApp just now to see how it works nowadays, and it’s still the same as it was before: nags you to no end to enable full Contacts access (no, Meta, I’m not letting you dump my entire contacts database into your app so that you can data mine it). iOS lets you select a minimal set of contacts to give it, but if you do this, it still shows you a full screen saying to enable full contacts access before it will let you contact anyone. No thanks. (I deleted my account immediately again, maybe I’ll try again in another 5 years.)
I'm guessing you are a younger generation than I am. My friends group tends to use Facebook Messenger for this. I never use Facebook myself, but do use messenger for essentially texting people.