It's not one byte. Please learn about Unicode.

$chr() now returns Unicode codepoints. á is represented by codepoint U+00E1 or 225. As shown by the page, the UTF-8 encoding of this codepoint is 2 bytes long:

UTF-8 (hex) 0xC3 0xA1

Exactly what you get when you use it:

Code:
//bset -t &x 1 á | echo -a $base($bvar(&x,1),10,16) $base($bvar(&x,2),10,16)