misleading error message in ProcessUtilitySlow T_CreateStatsStmt

hi.

while reviewing other work, some error messages in src/backend/tcop/utility.c
seem not accurate.

static void
ProcessUtilitySlow(ParseState *pstate,
PlannedStmt *pstmt,
const char *queryString,
ProcessUtilityContext context,
ParamListInfo params,
QueryEnvironment *queryEnv,
DestReceiver *dest,
QueryCompletion *qc)

case T_CreateStatsStmt:
{
Oid relid;
CreateStatsStmt *stmt = (CreateStatsStmt *) parsetree;
RangeVar *rel = (RangeVar *) linitial(stmt->relations);

if (!IsA(rel, RangeVar))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("only a single relation is
allowed in CREATE STATISTICS")));
relid = RangeVarGetRelid(rel,
ShareUpdateExclusiveLock, false);
/* Run parse analysis ... */
stmt = transformStatsStmt(relid, stmt, queryString);
address = CreateStatistics(stmt);
}

for example:

create or replace function tftest(int) returns table(a int, b int) as $$
begin
return query select $1, $1+i from generate_series(1,5) g(i);
end;
$$ language plpgsql immutable strict;

CREATE STATISTICS alt_stat2 ON a, b FROM tftest(1);
ERROR: only a single relation is allowed in CREATE STATISTICS

this error message seem misleading?
also this error check seems duplicated in CreateStatistics?