Possibly, but it seems unlikely. Federal resistance along the Monocacy collapsed into a disorganized retreat. These men were moving rapidly to the southeast, attempting to reach safety inside the defenses of Washington DC. They weren't thinking about Confederate stragglers in the rear of Early's advance. The Federal garrison at Harpers Ferry was untouched, however, and scouts from Harpers Ferry probably came across Confederates attempting to follow Early's main body north over the Potomac at Shepardstown. It's more likely (as one card states) that WMF was captured by Hunter's forces operating out of Harpers Ferry.

Remember that WMF wasn't released at Richmond VA until June 25th. At that time Early's men had started down the Shenandoah Valley, reaching Winchester by July 2nd. In order to catch up, WMF would have to make better time than Early's advance. He may have been in company of other convalescents trying to return to regiments assigned to Early. Since late news about Early's movements was relayed by word of mouth, they probably didn't move along the most convenient route to intercept.

I'm suggesting that WMF may not have caught up with his regiment by July 10th.