TL;DR - That cable is probably NOT HDMI compliant, but likely still works.
As you said, you do need an active converter to convert from HDMI to Analog (VGA). Analog signals are not provided by HDMI.
However, some cables (like the one you linked) do not have an external power source. If that's the case, then they are powering from the HDMI cable themselves. The HDMI spec says that you can draw at most 55mA, which I believe is far too little for a VGA converter. I suspect that cables like the one you linked are not HDMI-compliant, but still may work.
Note: here's what the HDMI association has to say on it:
Q. If an HDMI accessory device (i.e. switch box, cable booster) does
not have a dedicated power supply, is it still compliant and will it
An HDMI device that has active electronics should have a
provision for external power in order to be compliant (e.g. a
receptacle to allow the use of a standard power adapter, sometimes
called a power “brick”). Here we are drawing a distinction between
“active” devices that actually have some powered electronics, and
“passive” devices, such as some switches (more on those later).
Some active devices, such as actively powered HDMI cables or in-line
signal extender boxes, will by default attempt to power their
electronics by taking power from the 5V line (+5V power) available on
the HDMI connector. The HDMI specification requires all source devices
to provide at least 55mA (milliamps) on the 5V line for the purpose of
reading the EDID of a display. While 55mA is not enough current to
operate most HDMI accessory devices (which typically require about 100
to 150mA), most source devices on the market today provide
significantly more current on the 5V line than the HDMI specification
requires. As a result, the vast majority of accessory devices can
operate when interfaced with a source device that provides more than
the required current (i.e. over 100-150mA) on the 5V line. However,
manufacturers should provide a provision for their powered HDMI
accessory devices to obtain external power, and consumers are
encouraged to look for this external power provision when purchasing
Looking to the future, not all HDMI devices may provide this much
power over the 5V line. For example, as HDMI expands into more and
more portable applications (cameras, camcorders, laptops, etc.), power
consumption is often much more of an issue, and such devices may not
power the 5V line with the > 100mA required by such “active” devices.
Again, consumers should consider ensuring that their active HDMI
accessory device purchases have a provision for external power for
Total speculation: it's reasonably likely that the Raspberry Pi wires the 5V HDMI directly to the Pi's 5V input. If so, the VGA converter will have power equal to 1A minus whatever the Pi uses.