OP doubled his FIAT.
yep im knitpicking wording
but selling his 0.1btc means he has no btc and didnt increase 0.1 to 0.2
he instead bought 0.1, kept 0.1. held and done nothing.. and just cashed out.
You are technically right about that but it is still an investment and nothing can take that fact away that OP did double his/her investment. But you are right, OP could have made more if he/she doubled the bitcoin instead of cashing it out based on the fiat equivalent. Congratulations to OP for getting a big profit out of it, I hope that there is no regrets when you sold it at 30k price point because we are currently pushing a 50k point.