I have to believe that the 22ep22 was indeed sealed with frit glass. We are aware that the RCA 21cyp22 was first available in the CTC7 series sets. This RCA data sheet for the 21CY shows a date of 8/57
http://www.mif.pg.gda.pl/homepages/f.../2/21CYP22.pdf
Based on the date of this link at ETF showing the photo of the 22ep22
http://www.earlytelevision.org/color_crts.html dating the crt at around 1957 I should think that frit was used to seal the 2 piece envelope.
I do not think any method of heating to the point that glass will fuse to itself could work. There are too many issues that could produce uneven stresses in the glass.
KISS principal: frit was available, why try to do something much more difficult.
The fact that you cant see the usual frit line, as a person would see on a 21cyp22, doesn't necessarily mean that frit is not present on the joint and can not be seen.
I don't know what sort of a joint was used in the 22EP22. It could possibly be hidden beyond what you can see by external visual examination.
And thanks for the link to the excellent photo of the side of your 22EP22!
Just my thoughts.