From the video, it sounds like he engineered his own cells. Using a virus that is known for transferring genetic material into other organisms, he added a gene for producing lactase, and then ate it. I suppose that would affect both his gut bacteria and his own cells. But it lasted for ~1.5 years, which probably indicates that it truly was his cells. Also he seems to know what he's talking about, and he claims it was his own cells.

You're right, thanks!

Could be placebo though?

Is there a reason why I'm seeing squares between each of the characters in your message? It's making it pretty hard to read...

I'm using Chrome on Android

Firefox on iOS, I see strikethrough but the strikes are at varying heights.

The text is crossed out using Unicode combining characters of a strikethrough. This allows it to display without any specific formatting support, but it does require that the font support those characters. The font you're using doesn't support the characters, so it displays boxes, instead.