Even though many would say Cantonese (Even HK people do)
It's actually HK variant of Cantonese with many HK unique phases
The Cantonese in Guangzhou is quite different
I am not sure why you have such assertion, all the people speaking Cantonese dialect whether from China (including Hong Kong and Guangdong Province), or from Malaysia, Singapore or Indonesia can communicate and understand each other. There isn't any significant difference. [1]
If you really want to talk about varieties of Chinese then its quite a complex topic.
"Classifications of Chinese varieties in the late 19th century and early 20th century were based on impressionistic criteria. They often followed river systems, which were historically the main routes of migration and communication in southern China. The first scientific classifications, based primarily on the evolution of Middle Chinese voiced initials, were produced by Wang Li in 1936 and Li Fang-Kuei in 1937, with minor modifications by other linguists since. The conventionally accepted set of seven dialect groups first appeared in the second edition of Yuan Jiahua's dialectology handbook (1961):
1. Mandarin
2. Wu
3. Gan
4. Xiang
5. Min
6. Hakka
7. Yue
The Language Atlas of China (1987) follows a classification of Li Rong, distinguishing three further groups:
8. Jin
9. Huizhou
10. Pinghua
Some varieties remain unclassified, including the Danzhou dialect of northwestern Hainan, Waxiang, spoken in a small strip of land in western Hunan, and Shaozhou Tuhua, spoken in the border regions of Guangdong, Hunan, and Guangxi.
"
It's true that the language enunciation is very close for Cantonese speakers, but it's the phrases used that are quite different.
Mainland Mandarin vs. Taiwan Mandarin for example ~ there are a ton of phrases, especially for modern things like "credit card", "take out"..., that people use different words/phrases for. This is also the same for HK Cantonese vs. Cantonese used on the mainland where there was no British influence.
No one calls it HongKongese b/c it is not that different, you're exaggerating. Not all people in Guangzhou can speak Cantonese and those who can, even if they are native speakers, might not accent-savvy enough to tell an HKer if he/she tries to avoid some unique phases.
