The short arms are concerning, but his 'catch radius' is 48th percentile amongst WRs who tested (versus Hunter Renfrow's 25th percentile, for example).
I'm not saying this is the be all, end all but I thought it worth mentioning. He maybe an outlier due to his athleticism:
Catch Radius – first discussed by Scott Smith in a piece titled “The Catch Radius Project: In Search of Better TD Production”, the metric incorporates a player’s ability to cover ground as well as his ability to get vertical in order to score a player’s capacity to reaching the football in a 3-dimensional space. Catch Radius affects a player’s ability to succeed in the red zone, particularly on fade routes and 50-50 balls. The equation squares a player’s 40-time, 20-yard shuttle, and 3-cone and multiplies it by the square of a player’s height, arm length, and vertical jump. The values of all six data inputs are normalized to have equal weight.