Why would my employer randomly contribute a one-time, mid paycheck $1,100 to my 401k?

Checked my Fidelity recently and saw a contribution of ~$1,100 made mid paycheck from my employer. I had recently adjusted my contribution to 6%, which is their max match %.

Are they adding the other 2% from all previous paychecks to match the 6% total? I just can't think of another reason they would contribute so much at once.