Possible but unlikely. If a foil card is supposedly 1/100 then you should expect 3 foil cards in every million booster packs.

Possible, yes. The cards you get from boosters are totally random and include the foil versions too.
But to get 3 foil cards in a booster drop would be an insane amount of luck, thats a 1 in multiple millions chance.
In 14 years on Steam i seen someone ONCE get 2 foil cards from a booster but never three.

whatever 'friend' told you this is lying

I got 2 Foils once, never 3.

It is possible. but I only managed to get 2 foils in a single pack 3 times.

1st time: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1765440690
2nd time: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2001676966
3rd time: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2837273756

Given the number of users of steam, presumably someone somewhere comes up with the 1 in a million shot on a regular basis, just like it is very unlikely you will win the lottery jackpot even for an entire lifetime, but there are enough people playing each week that someone wins most times.