i5-750 + RX 580 8GB here, usually game hovers around 160 when im mid action. I run win7 with no other programs but CS and Steam open. Never had an issue with FPS since I upgraded from my Pentium E5800 back when I first started playing.
It isn't this code is probably in reference to when steam accepted bitcoin payments and therefore you could buy keys and other items via steam with bitcoin before transaction fees got too expensive and they removed support. You can't really gain anything mining bitcoin with cpu's and gpu's if there was a crypto miner you would see references to "monero randomx ethash cuckoo cycle" but not bitcoin.
Could've gotten it through some sketchy workshop map or server. Only way to legitimately get the right answer is to check on a new windows with a new steam account and launch cs.
I doubt Valve would be stupid enough to try and pull this besides many old PC's can run the game smoothly with a lot of fps so it's unlikely they are getting mined for BTC during gameplay.