Here's how spot-welding works. If you take a close look at how your car's unibody is held together, there are thousands of those little dimpled spots everywhere. Spot-welding is very fast and efficient production method. No filler-rods needed, no clean-up, etc.



However, due to the non-uniform contact area, it's not as optimized a solution as seam-welding or brazing around the end of the tubing for lightweight designs. In this case, there's enough material in that area so it's fine for the intended usage.

Echo's a department-store brand seen at Sears, K-mart, etc. They also have accessories like tubes, helmets, pedals, etc. Sealing the gap with silicone will work, just make sure to clean off all grease and dirt beforehand.