The specs of the Mac's charger can be seen on this image:
According to Wikipedia the USB specification is:
USB supplies power at 5 V ± 5% to power USB downstream devices. (source)
5% of 5V are 0.25V
Therefore any USB device have to be able to work correctly as long as the "received" power via USB is within the range of 4.75V to 5.25V.
The Apple USB power supply with 5.2 Volt is within this range.
Yes, you safely can charge
The Mac Charger follows USB Power Delivery (USB PD) as you can see in the picture you pasted.
USB PD is a different standard from USB Type C, in that it supports broader charging specs which was initially based on profiles and later evolved to Power Rules. These are well explained in What are USB PD Power Rules?. Quoting relevant extract :
The new rules also introduce a “superset” guarantee. Larger wattage power sources must support all voltage levels below their maximum up to 3A. As the spec says, “Bigger is always better in user’s eyes – don’t want a degradation in performance. Higher power Sources do everything smaller ones do”
As a result, the consumer only needs to know that their device ships with a x watt power supply, and know that any power supply that is rated at > x watts will be at least as good as the one that shipped with the device.
- Also see the questions at the bottom of the 87W charger you linked. It talks of an iPhone charging (Can the 87W USB-C power adapter be used with the NEW iPhone Xs Max? and will it damage the Xs Max?) which supports this (while mechanics of iPhone charging are different, the standard is the same)
Related from SE.Ask Different which confirms what I said Is the Macbook 12 inch's USB-C charger interchangeable with other USB-C chargers or devices? - this is in the context of USB Type C charging and the same logic holds and more strongly for USB PD.