So that answered my question, he did this intentionally.
Yes, the two times I have seen it they replaced a clear glass with a Redline tube, so they are teaching and improving the engine at the same time. They show us how to cut the glass and seal the tube and the proper way to warm the glass being the boiler is already warm and full of steam.
Interesting, thanks Nick.
I think I would stand back a little after replacing the glass under pressure... at least the first couple times trying it...
The procedure for when it breaks is to remember that the most danger comes from the water in the boiler... shield yourself with a shovel, clothing, or anything laying around, turn the water (bottom) off first, then the steam (top), check water level with try cocks, cut/install new glass, warm glass by opening the water glass drain cock and cracking open the steam valve, after a few seconds, close the drain cock and slowly open the water valve, then fully open the steam valve. Never tighten packing nuts with either valve open.