Boilers should fill automatically with makeup water. You do not fill them by other means.

Read the boiler manual- if you bled the rads, did you just open bleed valves at each one until there was no air? Or did you see water pouring out, it slowed down and then stopped, indicating zero pressure? If the latter, the boiler may have sensed a leak/low pressure and shut down so you have to restart it- it may have closed a solenoid that shuts off the line to the front-mounted gauge on the boiler. Did you lock out or shut off the boiler when you did this? There should be an automatic spirotop-type bleeder and you shouldn't need to do this at all; there is almost certainly one in the boiler- Viessmann boilers tend to accomplish every feature within them. But these things can get deposits in their vent and become blocked- a plumber needs to tend to that. Don't monkey with a fancypants boiler like this.

The grey hose and corrugated line all leads to drain- that's where excess pressure/condensate, etc. goes. You have 7 bar of pressure in the supply lines- did you close that angle stop handwheel when bleeding the rads and forget to open it?

Some gauges are not reading all the time and need to have a valve before them opened to read pressure. Does this boiler heat your tap water via a pump and heat exchanger in another tank and also feed your radiators? are you sure there are no other lines coming out of the boiler?