The dividends & capital gains distributions that Fidelity did at the end of the year (even though you did no action yourself) may certainly cause Cap Gains calculations. The fact that you re-invested-rolled back those distributions is immaterial. Those reinvestments are treated as-if you received the $$, then bought more. But the $$ re-invested do add into yoru basis for that mutual fund, that you will not be taxed on if you sell the mutual fund in the future.
Mutual Fund distributions normally are sent to you on a 1099-DIV form.
Anything in box 2a is a LT Cap Gain, and taxed as such at whatever LT Cap gains rates your total tax picture puts you into.
Anything in box 1a,1b is either a dividend.....or a ST gain distribution from the mutual funds, that is treaded as if a dividend.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
