I just stumbled on this buried treasure in OracleDialect:

			case Types.DECIMAL:
				if ( scale == 0 ) {
					switch ( precision ) {
						case 1:
							return jdbcTypeRegistry.getDescriptor( Types.BOOLEAN );

Of course, precision==1 means one decimal digit of precision, not one bit.

Now, just by pure luck, this doesn’t break anything because in Oracle pre-23c, we map BOOLEAN to number(1,0), but by the same token that whole block of code looks just completely pointless.

I believe it should be deleted.