Does DisplayPort 1.2 support HDR?

No it does not, not sure what those manufacturers are trying to say in the specs. But it is clear 1.2 does not support HDR.

Both models also says this:

"The HDR Effect helps transform non-HDR content into high quality video that looks like HDR through its picture quality algorithm."

No wonder you are confused, maybe contact LG and see what kind of explanation they give.

Source

So does DisplayPort 1.2 support HDR?

DisplayPort 1.2 does not support the hardware implementation of HDR 10.

However, the display still supports HDR, by using a software based implementation. The HDR mode will only be possible with compatible software. I have a suspicion this software compatibility would require AMD FreeSync to be used (although that’s not specifically stated)

The LG 27UK650 is also compatible with HDR10 content even if it doesn’t carry the necessary requirements. The HDR mode will automatically activate if the monitor receives a compatible signal, but the device only relies on a software-based implementation. When active, the HDR representation adds a nice touch of extra color pop and a seemingly deeper contrast range, although the monitor’s limitations will come into play here.

Source: LG 27UK650

From the Wiki: 'Refresh frequency limits for HDR video[edit] Color depth of 10 bpc (30 bit/px or 1.07 billion colors) is assumed for all formats in these tables. This color depth is a requirement for various common HDR standards, such as HDR10. It requires 25% more bandwidth than standard 8 bpc video.

HDR extensions were defined in version 1.4 of the DisplayPort standard. Some displays support these HDR extensions, but may only implement HBR2 transmission mode if the extra bandwidth of HBR3 is unnecessary (for example, on 4K 60 Hz HDR displays). Since there is no definition of what constitutes a "DisplayPort 1.4" device, some manufacturers may choose to label these as "DP 1.2" devices despite their support for DP 1.4 HDR extensions.[49] As a result, DisplayPort "version numbers" should not be used as an indicator of HDR support.' The 650/850UK's are 4k @ 60Hz only, so this would make sense.