Do these Muslims all claim to have seen and been personally insulted by the image? No. Do they even know what the image shows? Perhaps, but there's no evidence of that. All we seem to have is an accusation being made on top of already-existing anger and outrage - and, presumably, poor relations between Buddhists and Muslims.
At least, I hope the relations between the communities was already poor or fragile. If this is how Muslims in Bangladesh treat people they already like, I'd say it's time for every non-Muslim to flee the country and find somewhere safer to live.
"We brought the situation under control before dawn and imposed restrictions on public gatherings," said Salim Mohammad Jahangir, Cox's Bazar district police superintendent. ...
Sohel Sarwar Kajal, the Muslim head of the council in the area where the arson took place, said he was trying to restore communal peace.
"We are doing everything possible to quell tension and restore peace between the communities," he told reporters.
Source: Reuters
Not all Muslims can be blamed for this, but Islam and the culture which it has fostered in this region can certainly be held as being partially responsible. Just about every religion objects to some degree to things labeled as blasphemous or insulting, but Islam has been going to much greater lengths in this regard.
Put bluntly, Islam in many places is causing people to be killed over alleged insults. This means religious feelings are being made more important than human lives, which is putting Islam in these places in the category of anti-human and anti-life ideologies. No ideology which says that human lives are worth less than someone's religious feelings or religious beliefs is a system that deserves even a modicum of respect.