120V double tapped main

Never seen this before and I’m reporting it as a defect, but what’s the implication here?

This was in a 1929 Condo building, and the electrical has been updated. Tthe sub in the apartment was modern with AFCI breakers and a perfect install, but then I get down to the basement to look at the remote service panel and see this.
Meter directly below the service panel, and the only wires feeding the main were 1 ungrounded wire (red) and1 grounded wire (white). The hot conductor was connected to the main breaker and under that termination was another black wire that looped right to the other pole on the main breaker. There is only one other double breaker in the panel (above the main breaker), and it is the disconnect feeding the sub panel in the apartment. Those connections were fine.

Is the following statement correct?
This is 120V service and by looping to the other pole on the breaker, it would power the other bus and this way the breaker for the sub believes it is “receiving” 240 volts.
Is there anyway this is safe?
Is the “double-tap” on the upper pole of the main breaker a safety hazard?
What is the fix if there are only 2 wires coming from the meter?

None of this looks right so I am going to report it as such and recommend an electrician, but I’d like to understand it more and I’d also like to know if there is anyway I’m mistaken.

I probably should have mentioned that there were no 240 volt breakers in the apartment sub panel or any 240 appliances (stove was gas, and heat/hot water were HOA provided). The disconnect for the subpanel (in the service panel) was the only 240 volt breaker, but I feel like that is reason enough for me to recommend upgrading to 240 volt service.

That breaker lug is for one conductor only.

What size conductor is the red wire? Looks too small for 60 amps.

The neutral for that panel is no larger than a #10.

More than enough to defer.

You’re correct Robert, it was too small…I included that in my report as well. That I was sure of. Thanks for mentioning it though, making sure I didn’t miss it. I also was confident two conductors under the one lug was a defect, although I see I rambled and asked that as I was typing out my thoughts in the OP.

Really my biggest question is what it is doing when the 120V of service is shared across the two poles on the breaker? What is passing through the breaker disconnect for the sub panel above it? The building had 240V service entering it and assuming all 3 conductors make it to the meter bay were all the apartment service panels are located…is this likely to be a simple fix updating the service conductors between the meter and the panel?