Stimson, who took Dickson off minutes later, told BBC Radio Kent: "Chris has got pace, he's running into space so why shoot from there?
"It's an amazing decision and you can see where the ball ended up."
He added: "For the next two minutes he was worried about the shot that went over and their centre-half stepped in at least two or three times and cleared balls, so I'm disappointed."
Stimson pursued the Charlton striker for two years before he finally signed a three-month loan deal in February.
But the Gillingham boss has openly said how disappointed he has been with some of Dickson's performances during this second loan spell at Priestfield.
Source: BBC Sport
Source: BBC Sport