My opinion is that you should have moved a little.
First of all, ......If you droped anchor 75 feet from shore and let out 100 feet of rode..... I'll guess you were counting on a current to keep you off the rocks??
But back to the question......
We all were inexperienced at one time. We've all had bad days. We all have made mistakes as to "how far away" another boat is. We have all have had to anchor some place for the first time. And if he were concerned, expressed it politely or not, you had the oportunity to be the bigger man. Was there a reason you had to anchor exactly where you did? Was there no room to move a little?