Later during a campaign visit, he was taken to task by a voter who challenged his Conservative Party over a spoof website to distract voters from the opposition Labour Party's policy program.
Johnson's Conservatives are leading Labour in opinion polls, with Brexit and the future of the country's public health service the two most prominent campaign issues.
During an interview on Monday, a reporter from ITV repeatedly tried to show Johnson a picture on his phone of a 4-year-old boy lying on a pile of coats in a hospital, which featured on the front page of the Labour-supporting Daily Mirror.
The newspaper said the boy had suspected pneumonia and had to be treated on the floor because there were no beds available.
Johnson initially avoided looking at the phone, and instead began describing his investment plans for the National Health Service (NHS) while also saying he had not had a chance to see the photo.
The reporter said Johnson then took his phone and put it in his pocket.
When challenged again, Johnson took the phone out, looked at it and said: "It is a terrible, terrible photo, and I apologize obviously to the family and all those who have terrible experiences in the NHS but what we are doing is supporting the NHS."
"On the whole I think patients in the NHS have a much, much better experience than this poor kid has had," he added, before saying: "I am sorry to have taken you phone."
Opposition parties were quick to share the footage on social media, saying it showed Johnson did not care about patients.
BBC Political Editor Laura Kuenssberg said on Twitter health minister Matt Hancock was sent to the hospital in Leeds where the boy was pictured. He was greeted by a group of protesting Labour activists, she reported, one of whom punched his adviser.
Later, on a visit near the northeastern city of Sunderland, a target for the Conservatives, a worker asked him whether it was fear of Labour that made his party set up the spoof website.
"I'm afraid the short answer to that question is that I haven't got the foggiest idea," Johnson responded.
In regions of northern and central England which traditionally back Labour, Johnson hopes to break the party's hold on voters by appealing to those who backed Brexit.
But many in those areas have, sometimes for generations, rejected overtures from the Conservatives, and the worker was clear she felt the spoof website was a step too far.
Timed to coincide with the launch of Labour's manifesto, the website, www.labourmanifesto.co.uk, accuses the party of having "no plan for Brexit," proposing higher taxes and planning two more referendums.While stating that it is by the Conservatives, the site came at the top of Google search results on the day. Weeks later, it is still near the top.