Glue is probably contact cement and not a 'cold vulcanizing' glue which forms a much stronger mechanical bond between the patch and the tube.
If you can easily remove the patch that would confirm this theory. I use Victor 00599v cement which is described as vulcanizing and removing
patches put on with this glue is difficult and frequently leaves part of the patch still stuck to the tube. $6-7 for 8 oz, can lasts 4-5 yrs. (Walmart
or most auto parts stores).