I mean, that splitter device cannot be USB compliant, if it's giving more than 5V to a device that never negotiated more than 5V.
I'd also guess that if it's just silently feeding the second device from what the phone has negotiated, it's probably not compliant in that it's probably drawing more from its power source than the phone has negotiated -- USB devices are responsible for indicating what they'll draw.
You could make that multiport device USB-compliant, but it'd require having the splitter be a DC-DC power source and having it negotiate some PD draw sufficient to power both devices.