Why did he wait till encountering IFR to engage the autopilot?
Possibly means the Upper Modes; ie, Heading/Altitude holds etc. Our AP is engaged all the time by the holds aren't.
SOP is to engage the holds in the event of in-advertant IMC. This caused a problem with one operator a few years ago, when the pilot entered cloud, engaged the holds and the heading defaulted to North(as it was designed to), and the aircraft started turning, which the pilot wasn't expecting.
Due to low hours on type, instead of pressing the button to turn the holds off, he dumped the AP and the SAS an ended up with a totally unstabilised aircraft. They ended up in an untidy heap on the ground, fortunately without serious injury to the crew.
The heading hold(EC 135) has since been modded to take up the current heading when engaged.