ガセではない。IL表記ならこうだ。
.method public hidebysig instance void SampleMethod2() cil managed
{
.maxstack 3
.locals init (
[0] string s2)
L_0000: ldstr "1"
L_0005: stloc.0
L_0006: ldarg.0
L_0007: ldfld class [System.Windows.Forms]System.Windows.Forms.TextBox ImageComposer.Form1::textBox1
L_000c: ldloc.0
L_000d: callvirt instance void [System.Windows.Forms]System.Windows.Forms.Control::set_Text(string)
L_0012: ldarg.0
L_0013: ldfld class [System.Windows.Forms]System.Windows.Forms.TextBox ImageComposer.Form1::textBox2
L_0018: ldloc.0
L_0019: ldstr "\u3042"
L_001e: call string [mscorlib]System.String::Concat(string, string)
L_0023: callvirt instance void [System.Windows.Forms]System.Windows.Forms.Control::set_Text(string)
L_0028: ret
}