this is correct, international calls from home country are not affected by roaming regulation and cost more than same calls using foreign networks, they should regulate this as well, to make at least international EU calls from home country on par with roaming prices (aka domestic calls)
UK user in UK calls UK number – local country cost. UK user in Germany calls UK number - same cost as calling locally from UK. UK user in Germany calls German number – same cost as calling a UK number.
The weird edge-case is that calling a foreign number is less expensive when roaming; calling a German number from e.g. France is now cheaper than calling a German number from inside the UK, because the roaming regs affect roaming cost but do not affect what providers can charge for international calls from the home country.