'Hügel' is just the german word for 'hill'. There's no such word as 'Hugel' in german, the dots over the 'u' make it an Umlaut and all the difference in pronunciation between 'hügel' and 'hoogle'. The pronunciation of 'hoogle' in english and 'hugel' in german is the same.
There's a difference in all variations he wrote to have stumbled upon. For demonstration, the Google Translate tool pronounces it correctly using the Listen button on the left [1]. The correct one, 'Hügel', is different from both 'Hugel' and 'Hoogle', which can be pronounced as in English (cf., Google) and German (e.g., comparable to Woog [2]).
Even if the 'right spelling' is still wrong from the german word origin, hoogle is probably easier to pronounce in english than using 'huegel' and most certainly easier to type without the umlaut anyway.
Still, that remark ('[...] spent some time with google to find the right spelling') made me smile, as none of these variants are really correct.
I always think of the sound one makes when we say eeeeewww, as in 'that's disgusting', when remembering how to pronounce my ü's. I find that is a much closer sound compared to 'oo'.
Note that some dialects have their problems with the u-umlau, in which case you'll actually hear "Hugl". As the article is referencing someone from such an ü-challenged area (Mr. Holzer), maybe the writer just heard it that way.
