Disclaimer: just because a significant number of people in group A (esp. of a certain race/ethnicity) also have quality B does not mean that (i) all or most people of group A have quality B or (ii) people of group A who do not have quality B are in any way strange or inferior.
In other words, stereotypes are stupid; don’t apply them to real people.
The stereotypical “Asian” (a person from “Asia”, a mythical faraway continent consisting of two countries, China and Japan) is too hard-working, gets disowned for any grade below an A, has infinitesimally thin eyeslits, and pronounces L’s and R’s identically.
The internet says the L/R thing is mostly due to Japanese having only a single sound somewhere in between those two. Wikipedia has a page on Japanese phonology which seems to support this. Still, Wikipedia articles on phonology all consist of giving every sound a long incomprehensible name, such as the “apical postalveolar flap undefined for laterality” for the Japanese sound discussed above, and I’m not Japanese, so don’t take my word for it.
Mandarin Chinese (blatantly ignoring the myriad dialect variations) has a perfect L sound (ㄌ) and an R sound (ㄖ) that is only a little different. Of course, there are people who still pronounce them identically, but it’s not common — generally, the language teaches L’s and R’s well. Right?